FR2614311A1 - HYDROMETALLIZING AND HYDROCONVERSION CATALYST OF HEAVY HYDROCARBON FEEDING LOADS AND PROCESS FOR PREPARING THE SAME - Google Patents

Abstract

THE SUBJECT OF THE PRESENT INVENTION IS A CATALYST FOR USE FOR HYDRODEMETALLIZATION AND HYDROCONVERSION OF HEAVY HYDROCARBON FEEDERS. THE PURPOSE OF THE INVENTION IS TO OBTAIN A CATALYST HAVING GOOD DEMETALLIZATION AND HYDROGENATION ACTIVITIES. THIS AIM IS ACHIEVED WITH THE HELP OF A CATALYST INCLUDING A REFRACTORY SUPPORT INCLUDING A FIRST DEMETALLIZATION PHASE AND A SECOND HYDROGENATION PHASE PROVIDED THEREIN, THE FIRST PHASE OF DEMETALLIZATION BEING CHOSEN FROM HALF A FERMENTATION, ONE OXYY OF IRON AND MIXTURES THEREOF AND THE SAID SECOND PHASE BEING CHOSEN AMONG THE OXIDES OF IRON AND A METAL OF GROUP VIB, SULPHIDES OF IRON AND A METAL OF GROUP VIB AND MIXTURES OF THESE.

Description

2 614311

  Hydrodemetallization Catalyst and

  hydroconversion of hydrogen feedstocks

  heavy carbide and method of preparing the same.

  The present invention relates to an improved catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks, as well as to a process for the preparation thereof and relates more particularly to an improved catalyst comprising two distinct phases arranged on a refractory support, the first phase effectively retaining the metals removed from the feedstock and the second phase having a good catalytic hydrogenation activity during the treatment of feedstocks

  heavy hydrocarbon feed.

  Operations such as hydrogen treatment of heavy hydrocarbons have heretofore been carried out in the presence of catalysts comprising Group VIII and Group VIB elements arranged on a refractory oxide support. These types of catalysts have a number of disadvantages. For example, during the hydrogen treatment of heavy feedstocks, the life of most conventional catalysts is shortened by rapid deactivation. The first cause of deactivation is the deposition of coke on the catalyst. Coke deposits can be avoided by improving the hydrogenation activity of the catalyst. The second cause of the deactivation is due to metal deposits on the

catalyst.

  Most of the patents relating to improved demetallization catalysts relate to particular pore size distribution profiles of the catalyst. It has been found in the prior art that a catalyst having a macropore structure can generally accumulate larger amounts of metals. In order to obtain this macropore structure, several approaches have been proposed in the prior art. One of these is to vary the shape and size of the catalyst particles as well as the specific surface area and porosity of the catalyst support. Examples are found in the following patents: US-A-4,014,821, US-A-4,082,695, US-A-4,102,822,

  US-A-4,297,242, US-A-4,328,127, US-A-4,351,717, US Pat.

  No. 4,411,771, US-A-4,414,141. The optimum porous structure is well known in the art. As the optimum porous structure is established, the next step is therefore to optimize the preparation as well as the

chemical composition of the catalyst.

  Patents relating to variations in the preparation and chemical composition are as follows: US-A-3,898,155, US-A-3,931,052, US-A-3,985,684, US-A-4,344,867; and GB 2,032,795. The first three patents implement the incorporation of a third element in the catalyst that does not belong to the Group VIB and Group VIII elements. US-A-4 344 867 relates to a chemical treatment of a catalyst support. GB Patent 2,032,795 deletes the Group VIB element from the composition and proposes a method of impregnating the support for the preparation of the catalyst. All of these patents are however based on the fact that larger pores can accumulate larger amounts of metals. Thus, although some improvement in demetallization can be achieved by using these catalysts, the increase in demetallization is generally

  accompanied by a loss of hydrogenation activity.

  Accordingly, it is a principal object of the present invention to provide a catalyst and a method of preparing the same, the latter simultaneously having good demetallization and

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  of hydrogenation during the treatment of charges

  heavy hydrocarbon feed.

  A particular object of the present invention is to provide a catalyst and a method of

  preparation of it as mentioned above.

  above, the catalyst comprising two distinct phases at

  metal base, deposited on a refractory support.

  Another object of the present invention is to provide a catalyst and a method of preparing the same as mentioned above, the first phase being a demetallization phase and the second phase being

  phase being a hydrogenation phase.

  Yet another object of the present invention is to provide a catalyst and a process. of

  preparation of it as mentioned above.

  above, in which the weight ratio of the phases measured

  using a Mossbauer spectrum, is adjusted.

  Other purposes and advantages of this

invention will appear below.

  In accordance with the present invention, the goals are easily achieved and the

aforementioned advantages.

  The subject of the present invention is an improved catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks and a process for the preparation thereof and more particularly, an improved catalyst comprising two distinct phases disposed on a refractory support, the first phase effectively retaining the metals removed from the feedstock and the second phase having a good catalytic hydrogenation activity in the treatment of heavy hydrocarbon feedstocks. The catalyst of the present invention comprises a refractory support on which are disposed a first phase of demetallization and a second phase of hydrogenation,

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  the first phase of demetallization being selected from iron oxide, iron sulfide and mixtures thereof, and the second phase being selected from Group VIB iron and metal oxides, iron and aluminum sulfides. a Group VIB element and mixtures thereof, the weight ratio of the first phase to the second phase, measured with a Mossbauer spectrum being about 0.1 to 8.0, the iron being present in an amount of about 4 to 20% by weight and the Group VIB metal being present in an amount of about 0.1 to 8% by weight and the atomic ratio of iron to Group VIB metal being from about 0.3 to 20. According to a preferred embodiment of the present invention, the refractory carrier is selected from alumina, silica, titania and mixtures thereof, and has the following distribution of pore size: Diameter <90 A (10-10 m): 0 to 10% of pore volume Diameter 90 to 300 A (10-10 m): 20 to 85% of pore volume 300 to 500 A (10-10 m) diameter: 5 to 20% of pore volume Diameter> 500 A (10 -10 m): from 0 to 10% of the

pore volume.

  In the catalyst preparation process, a refractory support is provided, a first impregnation of the refractory support with an acid solution of iron nitrate so as to obtain a composition of about 4 to 20% by weight of iron in the final catalyst, filtered, dried and calcined impregnated support; a second impregnation of the filtered, dried and calcined iron-impregnated support with a solution containing a Group VIB metal component is carried out so as to obtain a composition of about 0.1 to 8% by weight of Group VIB metal component in the final catalyst, and filter, dry and calcine the impregnated support. In the process for treating heavy hydrocarbon feedstocks with the catalyst of the present invention, the feedstock is contacted with the catalyst of the present invention at a temperature of about 150 to 500.degree. a pressure of about 30.39.105 to 253.25-105 Pa and a liquid hourly space velocity (LHSV) of about 0.1

  at 25 h-1 inside a reactor.

  The catalyst of the present invention is capable of retaining metals removed from the heavy hydrocarbon feedstock in the demetallization phase disposed on the refractory support. The iron oxide phase and / or iron sulfide can accommodate significant amounts of metals without accumulating metals in the pores thereby avoiding a change in structure and a corresponding decrease in activity. The catalyst makes it possible to perform better demetallization and hydrogenation simultaneously compared to the catalysts

known until now.

  Simultaneous effective demetallization and hydrogenation of a heavy hydrocarbon feedstock can be accomplished using the catalyst of the present invention. The term "demetallization" (HDM) as used herein refers to the removal of at least 70% of the metals present in the heavy feedstock by passing the feedstock through a reaction zone containing

  the catalyst of the present invention.

  The catalyst of the present invention comprises a refractory support having a first demetallization phase and a second hydrogenation phase disposed thereon, the first phase of demetallization being selected from iron oxide, iron sulfide and mixtures thereof. of these, and the second phase being selected from Group VIB iron and a Group VIB metal, Group VIB metal and iron sulphides and mixtures thereof, the ratio of by weight of the first phase to the second phase, measured using a Mossbauer spectrum, being 0.1. 8.0, the iron being present in an amount of 4 to 20%, the Group VIB metal being present in an amount of 0.1 to 8% by weight and the atomic ratio of iron to the group VIB metal being about 0.3 to 20. According to a preferred embodiment of the present invention, the iron and the Group VIB metal are present in an amount of about 4 to 20% by weight and 0% by weight, the atomic ratio of iron to Group VIB metal being about 0.6 to 5.0. The first phase in the preferred embodiment contains from about 30 to 85% by weight and preferably. from 30 to 70% by weight of the total amount of iron present in the final catalyst and, when it is in the form of an iron sulphide, it must have a crystalline structure chosen from the cubic system, the hexagonal system, the

  monoclinic system as well as mixtures thereof.

  The crystalline structure of the first phase is important only when the phase consists of iron sulfide. If the phase comprises an iron oxide, the crystalline structure does not matter. This is because iron oxide is a precursor that forms iron sulfide under reaction conditions. The second phase preferably has a crystalline structure belonging to the cubic system and the atomic ratio of iron to the Group VIB metal is about 0.8 to 3.0. The preferred refractory support is selected from alumina, silica, titania and mixtures thereof, and has the following pore size distribution: <90A (10-10m) diameter : from 0 to 10% of the pore volume Diameter from 90 to 300 A (10-10 m): from 20 to 85% of the pore volume

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  Diameter from 300 to 500 À (10-10 m): from 5 to 20% of pore volume Diameter> to 500 À (10-10 m): from 0 to 10% of

pore volume.

  In order to obtain the two phases on the refractory support in the final catalyst, it is important that the support is first impregnated with the iron and then impregnated with the Group VIB metal. In the process of the present invention, a refractory support is provided, a first impregnation of the refractory support with an acid solution of iron nitrate so as to obtain a composition of about 4 to 20% by weight of iron in the final catalyst, filtered, dried and calcined impregnated support; a second impregnation of the filtered, dried and calcined iron-impregnated support with a solution containing a Group VIB metal component is carried out so as to obtain a composition of approximately 0.5 to 8% by weight of the Group's metal component. VIB in the final catalyst, and filter, dry and calcine the impregnated support. The method mentioned above makes it possible to obtain two phases deposited on the refractory support, the first phase consisting of iron oxide and the second phase consisting of iron oxides and a Group VIB element. If desired, the resulting catalyst may be previously sulfided to form iron sulfide and iron sulfide and a Group VIB element by prior sulfurization thereof at a temperature of about 250 to 450.degree. C at a pressure of about 1.01 x 105 to 151 x 95 x 105 Pa in an atmosphere of H2 and

  H2S containing from 5 to 15% by weight of H2S.

  The first phase of demetallization was characterized by its X-ray diffraction pattern and Mossbauer spectrum. The X-ray diffraction pattern of the first phase is used to determine the crystal structure of the precursor iron oxide or iron sulfide present in the presulfided catalysts. It has been found that only hexagonal, cubic or monoclinic iron sulfide crystals can retain the metals removed from the oil without loss of stability in that they have cationic vacancies that can accommodate the crude oil metal cations. The Mossbauer spectrum makes it possible to quantify the proportion or the ratio between the phases. The surface of the Mossbauer spectrum of any compound is proportional to its concentration. Thus, the integration of each spectrum of the different compounds present in

  a sample, provides the percentage by weight of those

  this. The first phase is characterized by a 6-peak spectrum while the second phase is characterized by a doublet spectrum. The Mossbauer spectrometry parameters of these two phases are included in the ranges

mentioned below.

  Field Displacement Magnetic analysis of quadrupole isomer Phase H (x10 4T) IS (mms-1) QS (mms-1) First (Oxide) 300 - 600 0.0 - 0.5 0.0 0.5 (Sulfide) 150 - 350 0.0 - 0.6 0.0 - 0.6 Second (Oxide) 0 0.0 - 2.0 0, 0 - 3.0 (Sulphide) 0 0.0 - 2.0 0.0 3.0 The examination of spent catalysts by Mossbauer spectroscopy reveals that the catalyst accumulates metal impurities from oil. The relative proportion between the two phases serves to adjust the activity,

9 2614311

  the stability (the service life) and the selectivity of the catalyst. The pore size distribution of the catalyst is only important to allow good diffusion of the reactive molecules through the catalyst, and is preferably as below. Diameter <90 A (10-10 m): 0 to 10% pore volume Diameter 90 to 300 A (10-10 m): 20 to 85% pore volume Diameter 300 to 500 A ( 10-10 m): 5 to 20% of the pore volume Diameter> to 500 A (10-10 m): from 0 to 10% .du

pore volume.

  A catalyst of the present invention is useful in hydrogen treatment operations by employing heavy feedstocks. It has a good catalytic activity for the reactions

  hydrodemetallization (HDM) and hydroconversion (HDC).

  Heavy feedstocks for use in these operations may be vacuum distillation residues, deasphalted crude oils

  and also heavy vacuum gas oils.

  In cases where it is desirable to use a presulfided catalyst, it should be presulfided with a feedstock containing low sulfur at temperatures of 250 to 450 ° C at pressures of 1.01. 105 to 151.95.105 Pa of H2. The H2 / H2S ratio is important as it maintains the ratio of the first phase to the second phase within the recommended limits. A mixture containing 5 to 15% H2S is suitable. H2S provides the sulfur compound in the presulfiding feedstock. Suitable sulfur compounds include H2S, CS2, mercaptans

  and / or any organic sulfur compound.

2614311

  The shape and / or size of the catalyst is not limited. Any shape or size can be used in a fixed bed reactor, stirred tank and / or slurry. The process comprises contacting the feedstock with the catalyst in the presence of hydrogen under the following conditions: a temperature of 150 to 500 ° C, preferably 250 to 480 ° C, a pressure of 30.39 × 10 5 to 25 ° C, 25.105 Pa, preferably from 50.65 x 105 to 151.95 x 105 Pa.

  and a LHSV (h-1) of 0.1 to 25, preferably 0.1 to 15.

  The present invention will be better understood on reading the following examples which are not given in

limiting title.

EXAMPLE 1

  A catalyst was prepared by sequentially impregnating granules with a carrier of -A1203. The iron impregnation was first carried out using an acid solution of iron nitrate containing 1.12 moles of iron per liter of solution. A volume of solution corresponding to twice the pore volume of the support was used. The catalyst was then thoroughly washed, filtered, dried and calcined. Molybdenum impregnation was then performed using an ammonium heptamolybdate solution containing 0.20 mol of molybdenum per liter of solution. Operations similar to those used for iron were then carried out. The final catalyst had the chemical properties

and subsequent physics.

  Physical properties Specific surface area 145 m2g-1 Pore volume 0.81 cm3 g1 Pore size distribution% pore volume Diameter (at (10-10 m)) <o90 8.5

-300 62.2

26.4311

he

300-500 23.7

> 500 5.6

  Chemical Properties Fe 6% by weight Mo 2% by weight The catalyst was ground up to an average size of 15 m and presulfided at 350 ° C. under a pressure of 1.21 × 10 5 Pa using a mixture of H 2 / H 2 S ratio of 1:10. The sulphurized catalyst was analyzed by

  X-ray diffraction and Mossbauer spectroscopy.

  The results indicate that two iron-based compounds are present, namely: hexagonal Fe7S8 40% of the total iron FexMoySz cubic 60% of the total iron i5 The following parameters of these two compounds were measured by Mossbauer spectroscopy: Field Displacement Magnetic analysis of the quadrupole isomer H (x10 = 4T) IS (mMs 1) QS (mms-1) Fe7S8 226 302 0.6 0.0 - 0.25 (6 peaks) FexMoysz O 0.3-1, 0.8 - 2.5 (2 peaks) The catalytic activity was determined in a 3.5 liter autoclave under the following conditions: Temperature 450C H2 pressure 131, 00.105 Pa Flow rate H2 16 1 / min (0 , 26 l / s) Time 5 h Catalyst 8% by weight Feedstock 1000 g The feed was a heavy residue of Zuata-type petroleum vacuum distillation, having the following properties: API Density 2.2 Sulfur content 4.9% D: 5 Vanadium content 750 ppm Asphalten content 25% by weight Carbon content Conradson 27% by weight The results are as follows: following states for the analysis of catalytic activity:

HDM 98

HDS (hydrodesulfurization) 70

Conversion rate of asphal-

  Carbon conversion rate Conradson 94 API 25.2 density variation With respect to the foregoing, the catalyst of the present invention proves to be very effective for the demetallization and hydrogenation of feedstocks.

heavy feed.

EXAMPLE 2

  The initial activity of the catalyst of Example 1 in the form of granules was evaluated, and a conventional commercial CoMo type catalyst having a similar pore size distribution and a Co content of 2.5% by weight. weight and a Mo content of 12.3% by weight in a Carberry reactor using the following conditions: Temperature 400 ° C H2 pressure 103.42.105 Pa Catalyst 6% Feed 600 g The feed consisted of deasphalted Morichal type oil having the following properties: API 16.7 'Density Vanadium content 150 ppm Sulfur content 2.4% by weight Asphaltenes content 2.4% by weight Carbon content Conradson 5 The two catalysts were subjected to three consecutive cycles of operation (with an xylene-intermediate wash) and were evaluated under the same conditions to determine the final activity of a partially deactivated catalyst. The results are summarized in Table I.

TABLE I

  Catalytic activity of the new Catalyst and a conventional catalyst FeMoAl CoMoAl Final Activity Initial Final Final

HDM 70 65 90 10

HDS 35 15 98 35

HDC540 + 75 100 65 34

  Asphaltenes Conversion 78 78 92 66 Conradson Carbon Conversion 50 61 55 As can be seen from Table I, the catalyst lifetime of the present invention is

  greater than that of known catalysts.

EXAMPLE 3

  An experiment similar to that of Example 2 mentioned above was carried out, but using three other feedstocks consisting of the same deasphalted oil diluted in a light gas oil in different proportions so as to obtain the following vanadium contents (ppm). ): Feedstock.1 150 Feedstock 2 100 feedstock 3 Vanadium removal (HDM) and conversion of the distilled fraction to a temperature greater than or equal to 540.degree. HDC540 +), the following results were obtained: Feed loads l 2 3 FeMo CoMo FeMo CoMo FeMo CoMo HDM Initial 75 92 78 94 80 95 Final 73 15 76 45 78 86 HDC Initial 85 70 88 75 92 80 Final 98 55 100 The superiority of the catalyst of the present invention is again demonstrated when the metal concentration in the feedstock is high.

EXAMPLE 4

  A series of catalysts such as D in Example 1 were prepared to obtain different ratios of

  first phase to the second phase, from iron to molybdenum.

  The catalysts have not been presulfided. The chemical composition of these catalysts is mentioned in

Table II.

TABLE II

Phase / First Second

  Catalyst Fe / Mo 2nd phase phase-phase

  Y-Fe 2 O 3 Y-FeMoO 4 2 8.0 4.5 c-Fe 2 O 3 *% - FeMoO 3 3.9 2.5 y -Fe 2 O 3 O-FeMoO 4 D 5 4 2.8 1.4 Y-Fe 2 O 3 -FeMoO 4 , 0 0.5-Fe 2 O 3 -FeMoO 6 0.9 0.0-C-FeMoO 4 -7 0.7 0.05-Fe 2 O 3 -FeMoO 4 8 0.4 0.08 D-Fe 2 O 3 -FeMoO 4 9 0.3 0 The catalytic activity and stability were evaluated in the same manner as in Example 2, but the catalysts were used in the oxidized form (as shown on the Table). II). your

  The results are shown in Table III.

TABLE III

  HDC Conversion Conradson Carbon Conversion HDM HDS 540+ Asphaltenes Catalyst

I F I F I F I F I F

1 10 8 2 2 15 13 10 8 7 8

2 54 52 18 17 56 54 68 55 25 24

3 62 58 19 20 65 67 73 62 32 29

4 68 64 20 19 70 72 75 73 48 46

71 65 24 15 75 100 78 78 50 60

6 92 38 43 12 88 25 95 42 82 28

7 90 55 40 16 84 52 92 50 75 36

8 86 70 39 20 83 61 88 78 70 42

9 84 73 39 20 80 68 86 65 68 49

86 25 33 12 80 20 88 18 70 20

I = Initial F = Final

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  Table III shows the importance of the ratio of iron to metal in Group VIB and the ratio of the first phase to the second phase for

  hydrodemetallization and hydroconversion.

EXAMPLE 5

  Catalyst No. 5 of Example 4 was presulfided with different ratios of H 2 S and H 2. The first stage iron sulphide had the structures

following crystalline

  N H2S / H2 Crystalline system First phase -1 1: 5 Cubic Fel_xS -2 1:10 Monoclinic Fe S y8 -3 1:15 Hexagonal Fe S eyS8 -4 1:20 Hexagonal FeS 55 1:30 Tetradic FeS Catalytic activity The initial results were measured in the same manner as in Example 2. The following results were obtained:

HDM HDS HDC540 +

-1 72 43 48

-2. 75 28 62

-3 85 22 39

-4 50 10 20

5-5 35 8 15

  The results mentioned above highlight the decisive effect of the crystalline structure

  of the first phase on the activity.

  Many variations and modifications may of course be made to the embodiment described above by way of example without departing from the scope of the present invention as

  it is defined in the appended claims.

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Claims (15)

  Catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks, characterized in that it comprises a refractory support comprising a first phase of demetallization and a second phase of hydrogenation disposed on the latter, said first phase of demetallization being chosen from an iron oxide, an iron sulphide and mixtures thereof, and said second phase being chosen from iron oxides and a Group VIB metal, the sulphides of iron and a Group VIB metal and mixtures thereof, the weight ratio of said first phase to said second phase, measured using a Mossbauer spectrum being from about 0.1 to 8, 0, the iron being present in an amount of about 4 to 20% by weight and the Group VIB metal being present in an amount of about 0.1 to 8% by weight, the atomic ratio of iron to metal of the Group VIB being about 0.3 to 20.   Catalyst according to Claim 1, characterized in that the iron is present in an amount of about 4 to 20% by weight and in that the Group VIB metal is present in an amount of about 1.0 to 5.0% by weight.   3. Catalyst according to claim 1, characterized in that said first phase comprises an iron sulphide having a crystalline structure chosen from the cubic system, the hexagonal system, the   monoclinic system as well as mixtures thereof.   4. Catalyst according to claim 1, characterized in that said first phase contains from about 30 to 85% of the weight of the total amount of iron in the catalyst.   5. Catalyst according to claim 1, characterized in that said first phase contains 18 2614311   about 30 to 70% by weight of the total amount of iron in the catalyst.   Catalyst according to Claim 1, characterized in that the atomic ratio of iron to metal   Group VIB is approximately 0.6 to 5.0.   3b 7. Catalyst according to claim 1, characterized in that said second phase has the crystalline structure of the cubic system and in that the atomic ratio of iron to the metal of Group VIB is from about 0.8 to 3.0.   8. Catalyst according to claim 1, characterized in that the refractory support is selected from alumina, silica, titanium oxide and mixtures thereof, and in that it has the size distribution following pores: Diameter <90 A (10-10 m): 0 to 10% pore volume Diameter 90 to 300 A (10-10 m): 20 to 85% pore volume Diameter 300 at 500 A (10-10 m): 5 to 20% of pore volume Diameter> to 500 A (10-10 m): 0 to 10% of pore volume.   9. Process for hydrodemetallization and hydroconversion of heavy hydrocarbon feedstock, characterized in that the feedstock is brought into contact with a catalyst comprising a refractory support comprising a first phase of demetallization and a second hydrogenation phase disposed thereon, said first demetallization phase being selected from iron oxide, iron sulfide and mixtures thereof and said second phase being selected from iron and metal oxides; Group VIB, Group VIB and Group VIB metal sulphides and mixtures thereof, the ratio by weight of that Group VIB. first phase to said 19 26-14311   second phase, measured using a Mossbauer spectrum being from about 0.1 to 8.0, the iron being present in an amount of about 4 to 20% by weight and the Group VIB metal being present according to an amount of about 0.1 to 8% by weight with an atomic ratio of iron to metal of Group VI D of about 0.3 to 20, at a temperature of about 150 to 500C under a pressure of about 39.105 to 253.25.105 Pa and with a liquid hourly space velocity of about 0.1 to 25 h'1 inside of a reactor.   Process according to claim 9, characterized in that the feedstock is contacted at a temperature of about 250 to 480 ° C at a pressure of about 50.65 x 105 to 151.95 x 105 Pa and with a speed of hourly space of the liquid of about 0.1 to 15 h-1.   11. Process according to revendicatiron 9, characterized in that the feedstock is a   heavy residue of vacuum distillation.   12. A process according to claim 9, characterized in that the feedstock is a deasphalted crude oil.   13. Process according to claim 9, characterized in that the feedstock is a gas heavy oil under vacuum.   A process for preparing a catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks, characterized in that it comprises the steps of: (a) providing a refractory support ; (b) impregnating said refractory support once with an acid solution of iron nitrate so as to obtain a composition of about 4 to 20% by weight of iron in the final catalyst; (c) filtering, drying and calcining said impregnated support; (d) impregnating said filtered, dried and calcined support a second time with a solution containing a Group VIB metal component so as to obtain a composition of about 0.1 to 8% by weight of Group VIB metal component in the final catalyst; and (e) filtering, drying and calcining said impregnated support.   15. Process according to Claim 14, characterized in that the impregnated support is sulphidized. obtained in step (e) above.